This invention relates to a power unit to be mounted on a vehicle, such as a three- or four-wheel vehicle, particularly to a power unit for a vehicle which is constructed by integrally joining an internal combustion engine and a transmission and adapted for use in a saddle type vehicle for off-road running as, for example, a so called a buggy vehicle.
As shown in FIG. 16 (refer to Japanese Laid-Open Patent Publication SHO 63-137087), most customary saddle type vehicles 01 have a power unit 02 with a crankshaft and transmission shafts directed in the vehicle width direction perpendicular to the running direction of the vehicle.
In the power unit 02 shown in FIG. 16, a case constructed by joining integrally a crankcase and a transmission case has bosses 04,05,06,07 for attachment at a front upper part, a front middle part, a rear upper part and a rear lower part, respectively, and the attachment bosses 04,05,06,07 are detachably attached to a vehicle body frame 08 through brackets 09. Therefore, in case of fitting the power unit 02 to the body frame 08 of the vehicle 01, a jig (not shown) is inserted in the hole of the boss 06 and a hanging piece (not shown) is engaged with a front lower end step portion 011 of a cylinder head 010 to suspend the power unit 02.
Because the saddle type vehicle 01 usually has a body frame 08 extending above the power unit 02, it is impossible to lower the power unit 02 suspended by the jig and hanging piece from above for fitting the power unit to the body frame 08 and, therefore, it is necessary to support the power unit 02 by two kinds of jigs and hanging pieces spaced in the width direction like a cantilever and bring the power unit into the vehicle laterally while moving the power unit in the width direction. Accordingly, the work of fitting the power unit was not easy.
On the other hand, as a power unit to be mounted on the saddle type vehicle with a crankshaft and transmission shafts directed in the vehicle running direction, hitherto, a power unit as described in Japanese Laid-Open Utility Model Publication SHO 63-125139 (ref. FIG. 17) has been known.
In case that the power unit with the crankshaft and transmission shafts directed in the vehicle running direction is fitted in the saddle type vehicle, it is necessary that tip end portions of the above-mentioned jig and hanging piece are bent at right angles; the bent tip end portions are moved in the vehicle running direction and engaged with the attachment bosses to support the power unit like a cantilever; and then the power unit is moved in the vehicle running direction. Therefore, the work of fitting the power unit was more difficult compared with the case of the saddle type vehicle 01 having the crankshaft and transmission shafts directed perpendicularly to the vehicle running direction.
In the power unit shown in FIG. 17, a cylinder block c, a cylinder head d and a head cover e are stacked on a crankcase b, in turn, and integrally connected to each other with a cylinder hole a of the internal combustion engine directed vertically. On the left of a crankshaft f positioned directly below the cylinder hole a is arranged a transmission shaft g; under the transmission shaft g an auxiliary shaft h; and on the right of the auxiliary shaft h and directly under the crankshaft f an output shaft i. Other shafts are arranged so as to surround the crank shaft f.
Further, on the right of the cylinder hole a is arranged a cam shaft j which is connected to the crankshaft through a chain-transmitting mechanism k. A push rod m is interposed between a rocker arm (not shown) and a cam follower l rocking up and down in response to the rotation of the cam shaft j and suction and exhaust valves (not shown) are opened and closed according to intermittent up and down motions of the push rod m.
In the customary power unit for vehicle of FIG. 17, a group of transmission shafts g, h, i are arranged in a region extending from the left to below of the crankshaft f and remaining shafts are arranged in a region extending from below to the right of the crankshaft f, so that the width in the left and right directions and the height of the crankcase b increase so that miniaturization of the power unit is difficult.
In addition, because the push rod-type cam-moving mechanism is arranged on the right of the cylinder hole a, the head portion of the power unit expands toward the right, so that when the power unit is installed in the vehicle, sometimes the power unit approaches too closely the inside of the thigh of the driver sitting astride a seat above the power unit.